vapor lock?

[nisan17]

I just had a scary situation with my 98 ML320. I was travelling a three hour non-stop trip in 100 degree temps up here in the north woods of Wisconsin, when during my last hour of travel I lost power when I tried to pass cars or when I gave it throttle over 65mph.

It seemed like bad gas or a plugged fuel filter. (never changed the filter in 1 1/2 yrs since purchase)
The next day after the temps dropped 20 deg. it ran great again. Any opinions as to what caused this?

The vehicle has 162k and has not had a major service from me. As soon as the season gets cooler I plan on doing a lot of maintainence myself. If the fuel filter is the suspect where is it so that I may change it myself?

Is it recommended to add fuel additive, and what kind?